Method and system for providing a single unified channel quieting/measurement request element in an 802.11 wireless local area network

ABSTRACT

A channel quieting/measurement request element is provided for use in a wireless local area network. The unified element of the invention integrates a dual capability for performing channel quieting and for making measurement requests of one or more stations in the network. According to another aspect of the invention, a conventional channel quieting element is modified to include provisions for defining an offset time and an offset duration interval for performing channel quieting.

CROSS REFERENCE TO RELATED CASES

Applicants claim the benefit of Provisional Applications Ser. Nos.60/362,971, filed Mar. 8, 2002 and 60/427,259, filed Nov. 18, 2002, andPCT International Application Ser. No. PCT/IB03/00837, filed Mar. 7,2003.

The present invention relates to wireless local area networks (WLANs).More particularly, the present invention relates to a method and systemfor providing a single unified measurement/quiet request element at theMAC layer in a WLAN.

A current mechanism defined in the IEEE 802.11h D1.1draft standard,January 2002, for performing measurements in an 802.11 based wirelesslocal area network (WLAN) is shown and described in FIGS. 1 a-c.

FIG. 1 a illustrates the format of a channel measurement request frame10 which is included as part of a spectrum management frame, for makingmeasurement requests in a wireless local area network (WLAN). Thechannel measurement request frame 10 includes, inter alia, a ‘channelmeasurement method’ element field for specifying a measurement requestelement. Two types of measurement request elements are shown in FIGS. 1b and 1 c, respectively.

FIG. 1 b illustrates a basic measurement request element 20 and FIG. 1 cillustrates a CF type measurement request element 30.

Presently, the IEEE 802.11 standard provides for a quiet channel elementwhich defines an interval during which no transmission shall occur onthe current operating channel. This interval may be used to assist inmaking channel measurements, like those specified in FIGS. 1 b and 1 c,without interference from other STAs in the BSS or IBSS. For example,the quiet channel element may be used to allow a channel to be testedmore easily for primary users without interference.

One drawback of the present scheme for quieting the channel is that thechannel quiet element may only be transmitted as part of a beacontransmission. This is restrictive in the sense that it may be necessaryto modify a most recently transmitted channel quiet element or otherwisetransmit a new channel quiet element between successive beacontransmissions so as to satisfy European DFS regulatory requirements foroperation in the 5 GHz band.

Another drawback of the current quiet channel element is that the quiettime specified in the element always starts immediately after the beacontransmission. It would be desirable, in certain cases, to start thequiet time sometime after the start of a beacon transmission at a timewhen radar transmissions are expected. In this way, it would not benecessary to quiet the channel for the entire beacon interval.

An additional drawback of the current channel quieting mechanism is thatit is not integrated or tied to the channel measurement element of FIG.1 a. This is problematic in that two frame requests are required,requiring synchronization in their respective transmissions.

It would therefore be desirable to add a capability to provide an offsettime to schedule channel quieting within a beacon interval therebyovercoming the restriction of having channel quieting always beginimmediately at the start of a beacon transmission. It would also bedesirable to integrate the channel quiet element and channel measurementelement into a single unified element thereby simplifying the MACprotocol and providing a more streamlined means of making ‘clean’measurements in the channel.

The present invention addresses the foregoing needs by providing aunified element for use in a WLAN, the element uniquely integratingcapabilities for quieting the channel and/or making measurement requestsof stations (STAs) in the network. These features are at present,separately provided in a channel quieting element and a measurementrequest (MRQ) element, respectively.

The format of the unified element of the invention, according to oneembodiment, includes a number of fields including: a “count” field forspecifying a number of beacon intervals that the channel quieting and/ormeasurement requests shall be repeated over. A second field referred toas an “offset” field which specifies, for each beacon interval specifiedin the “count” field, a time interval (i.e., offset period) measuredfrom the start of the beacon interval after which the STA shall halttransmissions and/or make measurement requests. A third field, used inconjunction with the offset field, referred to as a “quiet time” fieldfor specifying a time interval whose start time is measured from the endof the specified “offset” time. The quiet time specifies a time intervalinside of which the STA shall halt transmissions and/or make measurementrequests. Additional fields of the single unified element of theinvention include a “measurement ID” field for specifying specificmeasurements to be requested and a “Channel List” for specifying one ormore channels in which channel quieting and/or measurement requests willbe performed.

One advantage of the unified element of the invention is that, bycombining both channel quieting and measurement request provisions in asingle unified element, the MAC protocol is simplified. Anotheradvantage is the ability to transmit the unified element independent ofthe beacon interval thereby reducing latencies which are normallyassociated with channel quieting/measurement methods of the prior art.By reducing these latencies, European DFS regulatory requirements forWLANs operating in the 5 GHz band are more easily satisfied.

According to another aspect of the invention, there is provided achannel quieting element which includes an offset feature. The channelquieting element is essentially a conventional channel quieting elementmodified to incorporate an offset capability. Specifically, the channelquieting element includes two parameters not available for use with theconventional channel quieting element. A first parameter referred toherein as an “offset” parameter for defining an offset time which mustfirst expire in each specified beacon interval before channel quietingcan occur. A second parameter referred to herein as an “quiet time”parameter defining a time interval, starting from the expiration of theoffset time, in which channel quieting is performed. The combination ofthe offset time parameter and the quiet time parameter essentiallydefine a ‘window’ inside of which channel quieting is performed in eachbeacon interval.

An advantage of the channel quieting element of the invention is thatchannel quieting is more flexibly performed. That is, the offset featureprovides a capability for performing channel quieting at any point afterthe start of a beacon transmission. This capability may be used to quietthe channel at a time when radar transmissions are expected (e.g., nearthe end of a beacon interval) without the associated drawback ofquieting the channel for the entire beacon interval as is required in aconventional channel quieting element.

It is noted, that while the invention finds suitable application for usewith WLANS operating in the 5 GHz band, it is equally applicable for usein other bands such as the 2.4 GHz band.

A more complete understanding of the method and apparatus of the presentinvention may be had by reference to the following detailed descriptionwhen taken in conjunction with the accompanying drawings wherein:

FIG. 1 a illustrates the format of a channel measurement request framewhich is included as part of a spectrum management frame;

FIG. 1 b illustrates a basic measurement request element;

FIG. 1 c illustrates a CF type measurement request element;

FIG. 2 illustrates a representative network whereto embodiments of thepresent invention are to be applied;

FIG. 3 illustrates a simplified block diagram of an access point (AP)and each station (STA) according to an embodiment of the presentinvention;

FIG. 4 illustrates the format of a measurement/quiet request (MRQ)element according to an embodiment of the invention;

FIGS. 5( a)-(d) illustrate partial timelines for illustrating the effectof transmitting a unified element for the purpose of performing channelquieting and/or making measurement requests, according to an embodimentof the invention; and

FIG. 6 illustrates the offset parameter for use with the channelquieting element.

In the following description, for purposes of explanation rather thanlimitation, specific details are set forth such as the particulararchitecture, interfaces, techniques, etc., in order to provide athorough understanding of the present invention. For purposes ofsimplicity and clarity, detailed descriptions of well-known devices,circuits, and methods are omitted so as not to obscure the descriptionof the present invention with unnecessary detail.

The unified channel quieting/measurement/request element, as its nameimplies, contains parameters for performing channel quieting and/ormaking measurement requests in a wireless local area network (WLAN). Inaccordance with the unified element of the invention, a single channelelement provides a dual capability for quieting the channel for aprescribed number of beacon intervals and for a prescribed start timeand duration inside each beacon interval and/or for making measurementrequests for a prescribed number of beacon intervals and for aprescribed start time and duration inside each beacon interval.

FIG. 2 illustrates a representative network 200 whereto embodiments ofthe present invention are to be applied. According to the principles ofthe present invention, there is provided a single unified element 202which may be transmitted by the AP 205 to one or more STAs 210associated with the AP 205, to request measurements and/or to quiet theSTAs 210 for some number of beacon intervals. It should be noted thatthe network shown in FIG. 2 is small for purposes of illustration. Inpractice, most networks would include a much larger number of mobileSTAs 210.

Referring to FIG. 3, the AP 205 and each STA 210 within the WLAN 200shown in FIG. 2 may include a system with an architecture that isillustrated in the block diagram of FIG. 3. Both the AP 205 and STA 210may include a display 30, a CPU 32, a transmitter/receiver 34, an inputdevice 36, a storage module 38, a random access memory (RAM) 40, aread-only memory (42), and a common bus 41. Although the description mayrefer to terms commonly used in describing particular computer systems,the description and concepts equally apply to other processing systems,including systems having architectures dissimilar to that shown in FIG.3. The transmitter/receiver 34 is coupled to an antenna (not shown) totransmit desired data and its receiver converts received signals intocorresponding digital data. The CPU 32 operates under the control of anoperating system contained in the ROM 42 and utilizes RAM 40 to performthe frequency selection within a wireless local area network (WLAN), byenabling the AP to provide a new channel or wireless link for allstations (STAs) associated with its BSS.

With continued reference to FIG. 2, to make a channel quieting and/ormeasurement requests in accordance with the present invention, amanagement frame including the unified element of the invention istransmitted by the AP 205 to one or more STAs 210 in the network, whichare associated with the AP 205. The unified element 202 containsparameter values for instructing the STAs 210 on how to perform channelquieting and/or make measurements. The format of the unified element 202of the invention will be now be described in greater detail. In part II,a description is provided of a conventional channel quieting element,modified to incorporate an offset feature, as will be described.

I. Unified Element Description

Referring now to FIG. 4, the format of the element 202 of the inventionis shown. In addition to the “Element ID” and “Length” fields, theunified element 202 includes a “measurement time” field 43 which iscomprised of three sub-fields: a “count” sub-field 43 a for specifyingthe number of beacon intervals that the measurement shall be repeatedover, an “offset” sub-field 43 b for specifying the time interval in TUs(time units) starting from target beacon transmission time (TBTT) afterwhich the station (STA) shall not transmit, and a “quiet time” sub-field43 c for specifying the time interval in TUs starting from the end ofthe ‘offset’ that the STA shall not transmit. The unified element 202also includes a channel list field 45 for selecting one or more channelsin the network in which to make measurements, and a “Measurement ID”field 47 for specifying the one or more measurements to be made.

Examples of Unified Element Use

A number of exemplary general cases are described below which broadlyillustrate the functionality of the unified element 202 of theinvention. In particular, the specific cases were chosen to illustratethe inherent flexibility in making measurement requests and performingchannel quieting by varying one or more of the parameter values includedin the unified element 202 of the invention. It is to be understood,however, that the specific cases are not limiting, rather they areprovided as exemplary to facilitate a more complete understanding of theinvention.

1^(st) case:

In the first case, the unified element 202 of the invention is used onlyto perform channel quieting in a single beacon interval without makingany associated measurement requests.

With reference now to FIG. 5 a, there is shown a partial timelineillustrating the result of transmitting the unified element 202 for thepurpose of performing channel quieting over an entire single beaconinterval without including a measurement request.

In the present case, the current channel is quieted for an entire singlebeacon interval. A single beacon interval is selected by setting the“count” field 43 a of the Unified element 202 to one (‘1’). For ease ofexplanation, the second beacon interval 55 is arbitrarily selected asthe interval to be quieted.

In the present case, the current channel is quieted for the entirebeacon interval. This is achieved by setting two parameters. The firstparameter, referred to above as the “offset” field 43 b must be set tozero (‘0’). In so doing, channel quieting begins at a point coincidentwith the start of the beacon interval (Point “A”). The second parameter,referred to above as the “quiet time” field 43 c is set to a value equalto the duration of the beacon interval in time units (TUs), which is 100TU in the present case.

In the present case, no measurement requests are made. As such, the“Measurement ID” element 47 of FIG. 4 is not included.

The pertinent parameter settings for the 1^(st) case, discussed aboveand illustrated in FIG. 5 a, are summarized in the table below.

Measurement Time Channel List Channel Channel Count Offset Quiet TimeLength Number . . . Number 1 0 100 TU 0 N/A N/A N/A 100 TU is assumed tobe the length of the beacon interval2nd case:

In the second case, the unified element of the invention is used only toperform channel quieting in a single beacon interval without makingassociated measurement requests. The present case is distinguishablefrom the first in that channel quieting is performed only in a portionof the single beacon interval.

With reference now to FIG. 5 b, there is shown a partial timelineillustrating the result of transmitting the unified element 202 forperforming channel quieting over a partial single beacon intervalwithout making a measurement request.

Similar to that described above, to select a single beacon interval, the“count” field 43 a is set to one (“1”). To perform quieting only over apartial interval of the beacon interval, a non-zero offset value 43 b isrequired. The offset value can be any value in the range,0<offset<length of the beacon interval (e.g., 100 TU). For ease ofexplanation, an arbitrary non-zero offset value may be calculated assome fraction of the beacon interval:Offset value=0.2*Beacon interval=0.2*100=20  (1)When an offset value is utilized in the unified element 202 of theinvention, a corresponding parameter, referred to herein as the “quiettime” parameter must be defined. For ease of explanation, an arbitraryquiet time parameter value may be calculated as some fraction of thebeacon interval as:Quiet time=0.4*Beacon interval=0.4*100=40 TU  (2)It should be noted that the combination of the offset time parameter andquiet time parameter essentially define a window (e.g., start time andduration) inside of which channel quieting is performed in the beaconinterval. This window is labeled as “B” in FIG. 5 b.

The parameter settings for the exemplary 2^(nd) case, discussed aboveand illustrated in FIG. 5 b, are summarized in the table below.

Measurement Time Channel List Channel Channel Count Offset Quiet TimeLength Number . . . Number 1 20 40 0 N/A N/A N/A 100 TU is assumed to bethe length of the beacon intervalIn the present case, no measurement requests are made and as such themeasurement ID element 47 of FIG. 4 is not included.3^(rd) case:

The present case is distinguishable from the first two in that channelquieting is performed for an infinite number of beacon intervals. Thatis, once a unified element 202 is broadcast including a directive toperform channel quieting and/or measurements in an infinite number ofintervals, that request will be carried out in every beacon intervalthereafter until such time as a subsequent unified element 202 isbroadcast having a different directive.

With reference now to FIG. 5 c, there is shown a partial timelineillustrating the result of transmitting an unified element 202 forperforming continuous channel quieting over an infinite number of beaconinterval without making a measurement request. It is noted that FIG. 5 cis provided primarily to illustrated that the operations specified areto be performed in each and every beacon interval until a subsequentunified element 202 is received indicating otherwise. In the presentexample, the operation of performing channel quieting over a partialinterval without making associated measurements is shown, solely forpurposes of illustration.

To perform the channel quieting in a succession of beacon intervals, the“count” field 43 a is set to hex 0×FF in the illustrative embodiment.The remaining parameters are otherwise identical with those describedfor the 2^(nd) case for ease of explanation and will therefore not befurther described.

The pertinent field settings for the 3^(rd) case, discussed above andillustrated in FIG. 5 c, are summarized in the table below.

Measurement Time Channel List Channel Channel Count Offset Quiet TimeLength Number . . . Number 0xFF 20 40 0 N/A N/A N/AIn the present case, no measurement requests are made and as such themeasurement ID element 47 of FIG. 4 is not included.4th case:

In the fourth case, the unified element 202 of the invention is used toperform both channel quieting and making measurement requests. The dualoperations highlight the novelty of the inventive unified element 202.In the illustrative example, the dual operations are performed in aninfinite number of beacon intervals over a portion of each beaconinterval.

With reference now to FIG. 5 d, there is shown a partial timelineillustrating the effect of transmitting a unified element 202 forperforming channel quieting over a partial beacon interval while makingone or more measurement requests.

Whenever a measurement request is made, the measurement ID element 47shown in FIG. 4 is included in the unified element 202.

The parameter settings are identical with those shown above for thesecond case, however, there is also shown some exemplary settings forthe channel list and measurement ID element.

Measurement Time Channel List Channel Channel Count Offset Quiet TimeLength Number . . . Number 0Xff 0.2*BI 0.4*BI 1 1 N/A N/A

Measurement Measurement ID . . . . . . ID . . . 1 N 1 NMaking Measurements without Performing Channel Quieting

In order to exclusively make measurements without performing channelquieting, the quiet time parameter must be set to a value of zero (“0”).To specify one or more measurement requests, one or more measurementidentifiers must be included in the “Measurement ID” field of theUnified element 202.

In summation, advantages of the Unified element 202 of the inventionover prior art methods for performing channel measurement/quietinginclude a simplified MAC protocol, higher reliability in transmission bytransmitting one frame instead of two dedicated frames (a quieting frameand a management frame), flexibility for performing measurements andflexibility in scheduling quiet times. Furthermore, by providing aunified element with flexible measurement and/or channel quietingoptions, the possible existence of pre-existing primary users in thechannel may be more readily determined. This capability would facilitatemeeting the requirements imposed by the European Radio communicationsCommittee (ERC) and it would enhance the performance of an 802.11 WLANoperation in the 5 GHz band or other band range, i.e., 2.4 GHz. Itshould be apparent to those skilled in the art that this invention canbe easily extended to other frequency bands, such as 2.4 GHz, usingdifferent physical layer specifications, such as IEEE 802.11b PHYspecification.

II. Modified Conventional Channel Quieting Element

As described above, the unified element 202 of the invention providesadvantages of making flexible measurements by virtue of being able tospecify a variable offset time for either performing channel quietingand/or making measurement requests. Presently, this capability does notexist in the conventional channel quieting element as defined by theIEEE 802.11 standard. However, an offset time capability would bedesirable to incorporate into the conventional channel quieting element.Therefore, the present application further provides a ‘modified’ channelquieting element that provides an offset capability as described abovewith respect to the unified element 202. In other words, theconventional channel quieting element is modified to the extent ofincorporating two parameters, an offset parameter and a quiet timeparameter, as described above, to essentially provide a capability ofgenerating a channel quieting ‘window’ in each beacon interval. In sodoing, the channel may be quieted at a time when radar transmissions areexpected (e.g., near the end of a beacon interval) without theassociated drawback of quieting the channel for an entire beaconinterval as is required in a conventional channel quieting element.

FIG. 6 illustrates a partial timeline illustrating such an offsetcapability in a modified conventional channel quieting element. In theillustrated example, channel quieting is performed over a partial singlebeacon interval (e.g. the 2^(nd) beacon interval). The offset time isdefined identically to that described above. That is, the offset timedefines a time which must first expire in the beacon interval beforechannel quieting may begin. The offset time is labeled “A” in FIG. 6,and is included in the modified channel quieting element as a singleparameter having a value in the range of the beacon interval. Acorresponding “quiet time” parameter defines the length of the channelquieting ‘window’, labeled “B” in FIG. 6.

The modified channel quieting element of the invention, incorporatingoffset and quiet time parameters provides similar advantages to thosedescribed above with regard to the unified element. Specifically, theconventional channel quieting element as modified provides flexiblechannel quieting options by providing an offset feature embodied as twooffset related parameters. Specifically, the offset parameters define anoffset time and quiet time duration parameter which collectively definea channel quieting “window” providing a capability for performingchannel quieting over any portion of the beacon interval where radartransmissions are expected without the associated drawback of quietingthe entire interval.

The foregoing is to be constructed as only being an illustrativeembodiment of this invention. Persons skilled in the art can easilyconceive of alternative arrangements providing a functionality similarto this embodiment without any deviation from the fundamental principlesor the scope of this invention.

1. A method for performing channel quieting and making measurementrequests via a single unified channel quieting and measurement requestelement in a wireless local area network (WLAN), comprising:transmitting said element from a source node to at least one destinationnode in said WLAN; upon receiving said element at said at least onedestination node: determining, from a first parameter included in saidelement, a number of beacon interval periods in which said channelquieting and making measurement requests are to be performed;determining, from a second parameter included in said element, an offsettime defining a time which must first expire prior to performing saidchannel quieting and making measurement requests, the offset timestaring from a target beacon transmission time of each of the beaconinterval periods determined from the first parameter; determining from athird parameter included in said element, a quiet time defining a timeduration over which said channel is quieted and measurements areperformed; determining from at least a fourth parameter included in saidelement at least one measurement identifier for determining at least onemeasurement to be performed in accordance with making said measurementrequests; and performing the operations of channel quieting andmeasurement requests in accordance with said first, second, third andsaid at least fourth parameters.
 2. The method of claim 1, wherein saidoffset time is defined in transmission units.
 3. The method of claim 1,wherein said quiet time is defined in transmission units.
 4. The methodof claim 1, wherein said request element further includes a channel listdefining at least one additional channel in which said channel quietingand/or measurements are to be performed.
 5. The method of claim 1,wherein said parameters are reset in a subsequently transmitted elementfrom said source node.